1. Field of the Invention
The present invention relates to a steering damper device used in a small-sized vehicle such as a motorcycle. More particularly, the present invention relates to an improvement of a steering damper device in which a rotary damper includes a damper case, a rotary shaft rotatably supported on the damper case, and an actuation lever connected to an outer end of the rotary shaft, and is configured so that the rotary shaft is rotated to generate a damping force in the damper case; the damper case is mounted to a steering side member that is rotated around a steering stem by an operation of a handlebar; and a tip end of the actuation lever is connected to a frame side member that is not rotated by the operation of the handlebar.
2. Description of the Related Art
In a motorcycle, a front fork supporting a front wheel is rotated by an operation of a handlebar around a steering stem that is rotatably inserted into a head pipe at a front end of a vehicle body frame, to thereby perform steering. In some cases, such a motorcycle is provided with a steering damper device between a steering side member that is rotated by the operation of the handlebar and a frame side member that is not rotated by the operation of the handlebar. In such cases, the steering damper device is required to generate little damping moment in normal driving with a small steering angle of the handlebar and a low angular speed, to generate a high damping moment in a situation with a large steering angle of the handlebar and a high angular speed, to set a low damping moment in a situation with a low speed and a relatively large steering angle of the handlebar because of continuous small turns, thereby minimizing the load on the operation of the handlebar; also required to generate little damping moment when steering is returned. For this purpose, some of conventional motorcycle steering damper devices use an oscillating damper and have a bypass that changes a damping force in a complicated manner to meet the requirements described above.
However, such a steering damper device using the oscillating damper has a complicated structure and is expensive, large and heavy, which may sometimes restrict the arrangement of other components.
A motorcycle steering damper device comprising a rotary damper that has a simple structure and is inexpensive has been also known (for example, see Japanese Patent Laid-Open No. 2000-255473). The steering damper device is configured so that with a rotary shaft of the rotary damper being arranged coaxially with a steering stem, a damper case is secured to a front fork, a tip end of an actuation lever is rotatably connected directly to a vehicle body frame, and the rotary shaft is rotated to generate a damping force in the damper case at the time of steering.
In the device using the rotary damper described above, however, a steering angle and a rotation angle of the rotary shaft linearly increase proportional to each other, and thus a complicated control device needs to be added in order to meet the requirements described above.